Wideband antenna module for the high-frequency and microwave range

ABSTRACT

An antenna module more particularly for the high-frequency and microwave range is described which can be operated as a wideband antenna in various frequency bands. For this purpose the antenna module is particularly suitable in that it has an antenna ( 10 ) and an HF line ( 20 ) to connect the antenna ( 10 ) to associated transmit and/or receive stages, while at least parts or sections ( 21, 22 ) of the HF line ( 20 ) have a mismatch in the form of an impedance deviating from that of the antenna ( 10 ). The invention also relates to a telecommunications device having such an antenna module.

The invention relates to an antenna module, more particularly for thehigh-frequency and microwave range, which can be operated in thewideband or various frequency bands respectively. The invention alsorelates to a telecommunications device comprising such an antennamodule.

For transmitting information by particularly mobile telecommunicationsdevices, generally electromagnetic waves are used in the high-frequencyor microwave range. For transmitting and receiving these waves antennasare increasingly used which can be operated in various frequency bandseach having a respective sufficiently large bandwidth.

Such frequency bands are situated for example in the mobile telephonestandard between 880 and 960 MHz (GSM 900), between 1710 and 1880 MHz(GSM or DCS 1800), as well as particularly in the USA between 824 and894 MHz (AMPS), as well as 1850 and 1990 MHz (D-AMPS, PCS or GSM 1900).Furthermore, this includes the UMTS band (1880 to 2200 MHz), moreparticularly wideband CDMA (1920 to 1980 MHz and 2110 to 2170 MHz) aswell as the DECT standard for cordless telephones in the frequency bandfrom 1880 to 1900 MHz and the Bluetooth standard (BT) in the frequencyband between 2400 to 2483.5 MHz which is used for exchanging databetween various electronic devices such as, for example, mobiletelephones, computers, appliances using entertainment electronics etc.

It is also necessary at least in a time-dependent transition area formobile telephones to be operated both in at least one of the GSMfrequency ranges and in the UMTS frequency range. In many cases it isalso necessary for a mobile telephone to be operable both in the twoEuropean (GSM) bands and in the two US bands (AMPS and PCS), so thatusers who are often in the USA and in Europe need not carry along twomobile telephones.

In addition to the transmission of information, the mobiletelecommunications devices are also partly provided with additionalfunctions and applications such as, for example, for the satellitenavigation in the known GPS or another frequency range in which theantenna should then also be capable of operating.

Basically, it is necessary for modern telecommunications devices of thistype to be operable in a maximum number of these frequency ranges, sothat corresponding multiband or wideband antennas are necessary whichcover these frequency ranges.

Due to the increasing integration of these and further functions in amobile telephone and the simultaneous attempts to miniaturize them asmuch as possible, there is a further need for the antennas to have thesmallest possible volume and a smallest possible surface because thereis ever less space in the housings available.

In order to minimize the size of the antenna with a given wavelength ofthe emitted radiation, a dielectric having a dielectric constant ε_(r)>1can be used. This leads to a shortening of the wavelength of theradiation in the dielectric by a factor of 1/⊂ε_(r). Therefore, anantenna designed on the basis of such a dielectric is also reduced bythis factor. But a disadvantage of this is that with an increasingdielectric constant also the bandwidth of the antenna becomesaccordingly smaller.

An antenna of this kind comprises a substrate of a dielectric materialon the surfaces of which one or more resonant metallization structuresare applied as dictated by the desired frequency band or bands. Thevalues of the resonant frequencies depend on the dimensions of theprinted metallization structures and the value of the dielectricconstant of the substrate. The values of the individual resonantfrequencies then become lower as the length of the metallizationstructures increases and as the values of the dielectric constant becomehigher. Antennas of this kind are also referred to as Printed WireAntennas (PWA) or Dielectric Block Antennas (DBA).

A particular advantage of such antennas is that they, together withother components as desired, can be mounted directly on a printedcircuit board (PCB) by the surface-mounting (SMD) technique i.e. bybeing soldered flat to the board and by contacts being made in the sameway, without any additional mountings (pins) being required to feed inthe electromagnetic power.

Problematic and difficult, however, may be the dimensioning of themetallization structures particularly when such an antenna is to operatein a plurality of frequency bands. An optimum adaptation of the antennato one of the required frequency ranges results in that the antennapower in the other frequency ranges is affected because themetallization structures affect each other.

Another type of antenna which is also used in mobile telecommunicationsdevices are the what are called Planar Inverted F Antennas (PIFA) inwhich a metallization structure is disposed over a ground metallization,and which work as volume resonators. Detriments to these antennas are,however, that they either need relatively much space, which can bereduced only to a limited extent by the use of dielectric materials, orthat they have only a very narrow bandwidth in case of a reduced size onaccount of the strong interaction between different parts of themetallization structure.

An object on which the invention is based therefore consists in that anantenna is provided particularly for the high-frequency and microwaverange, which antenna, compared to the known antennas, has a considerablywider resonance curve for the frequency ranges mentioned above.

More particularly an antenna module is to be provided which is operablein at least two of the above-mentioned frequency ranges.

Furthermore, with the invention an antenna module of the type defined inthe opening paragraph should be provided which can be accommodated in arelatively small mobile telecommunications device that has a relativelylarge resonance bandwidth and relatively small dimensions and is thussaving space.

The object is achieved in accordance with claim 1 by an antenna modulehaving an antenna and an HF line to connect the antenna to associatedtransmit and/or receive stages in which at least parts or sections ofthe HF line have a mismatch in the form of an impedance that deviatesfrom the impedance of the antenna.

A particular advantage of this solution consists in that no additionalcomponents or assemblies such as, for example, passive impedanceinterface networks or active controls are necessary which both take upspace on the printed circuit board and would also cause additionalcosts.

A further advantage of the solution consists in that it can be appliedlargely independently of the type of antenna used and the operatingfrequency range provided. In this way, more particularly also thedifferent types of high-frequency and microwave antennas mentioned inthe opening paragraph can be given a larger resonance bandwidth.

The dependent claims have advantageous further embodiments of theinvention.

The embodiments as defined in claims 2 and 3 result in a particularlyeffective increase of the resonance bandwidth.

The embodiments as defined in claims 4 and 5 comprise an antenna whichcan be particularly advantageously used in the antenna module accordingto the invention.

The embodiment in accordance with claim 5 additionally offers itselfparticularly well for operating frequencies of about 2 GHz and over andhas the further advantage that a substrate may be dispensed with.

The claims 6 and 7 finally relate to a printed circuit board or a mobiletelecommunications device respectively having an antenna module inaccordance with the invention.

Further details, characteristics and advantages of the invention areapparent from the following description of exemplary embodiments of theinvention with reference to the drawing, in which:

FIG. 1A shows a diagrammatic plan view of a printed circuit board withan antenna module according to the invention,

FIG. 1B is an enlarged representation of an antenna of the antennamodule,

FIG. 2 shows the curves of the scattering parameters of the antennamodule with input structures of reduced impedance;

FIG. 3 shows the curves of the scattering parameters of the antennamodule having input structures of increased impedance,

FIG. 4 shows the curves of the efficiency of the antenna module withinput structures having reduced impedance; and

FIG. 5 shows the curves of the efficiency of the antenna module withinput structures having increased impedance.

FIG. 1(A) is a diagrammatic plan view of the front of a printed circuitboard (PCB) 30 having a metallization 31 which is preferably provided onits rear side. In a corner of the printed circuit board 30 in whichthere is no metallization 3 1, there is an antenna module having anantenna 10 and an HF line 20.

The antenna 10 is shown in enlarged form in FIG. 1(B) for clarity. Thisis a dielectric block antenna (DBA) or printed wire antenna (PWA). Theantenna module according to the invention, however, can also be producedwith other types of antennas, more particularly as explained earlier.Furthermore, the module can be dimensioned not only for the frequencyranges to be mentioned hereinafter, but also for other frequency rangessuch as those described earlier.

The antenna 10 comprises a substrate 11 which, in essence, has the formof a cuboidal block whose length or width is larger than its height by afactor of about 3 to 40. Therefore, in the following description theupper (large) face of the substrate 11 in the representation of FIG. 1is to be referred to as upper main face, the opposite face as lower mainface and the surfaces perpendicular thereto as side faces of thesubstrate 11.

Instead of a cuboidal substrate 11 is also possible to select anothergeometrical form such as, for example, a round or triangular orquadrangular cylindrical form depending on the application and availablespace. Furthermore, the substrate 11 may also have a hollow space orrecesses to save on, for example material and thus weight.

The substrate 11 is made of, for example, a ceramic material and/or oneor more plastics that can be used with high frequencies or by embeddinga ceramic powder in a polymer matrix. It is also possible to use purepolymer substrates. The materials should have the least possible lossesand a slight temperature dependence of the high-frequency properties(NPO or so-called SL materials).

In order to reduce the size of the antenna 10, the substrate 11preferably has a dielectric constant of ε_(r)>1 and/or a relativepermeability of μ_(r)>1. But it should be considered in this respectthat the bandwidth that can be achieved with substrates having a largeor increasing dielectric constant and/or relative permeabilitydiminishes.

With the antenna 10 shown in FIG. 1(B) the substrate 11 (preferably NPOceramic) has a dielectric constant ε_(r) of about 21.5 and a length ofabout 10 mm, a width of about 2 mm and a height of about 1 mm. Theantenna is suitable for wireless communication in the 2.4 GHz ISM band(for example Bluetooth, WLAN, home RF etc.).

The substrate 11 carries on its lower main face a resonant printedwiring structure 1 of an electrically highly conductive material suchas, for example, silver, copper, gold, aluminum or a superconductor. Theprinted wiring structure 1 could also be embedded in the substrate 11.

On the lower main face of the substrate 11 is disposed a first resonantmetallization structure 1 (dotted line) which is connected via a firstconnecting point 2 (solder point) to a ground potential i.e. groundmetallization 31. The metallization structure 1 may be formed by one orvarious individual metallizations in the form of printed wiring ofdifferent widths as the case may be. In the embodiment shown thestructure has in essence a meandering form over the entire length of thesubstrate 11 and has an electrically effective length L′ of L/⊂ε_(r)where L is the wavelength of the signal in free space. The metallizationstructure 1 is measured such that its length corresponds to about halfthe wavelength with which the antenna is to radiate electromagneticpower. For example, for the application of the antenna module in thefrequency range mentioned above between 2400 and 2483.5 MHz there is awavelength L of about 12.5 cm in free space. With a dielectric constant?_(r) of the substrate of 21.5 the half wavelength 0.5 L′ is shortened,and thus the necessary geometric length of the metallization structure1, to about 13.48 mm.

The resonant metallization structure 1 could also be embedded in thesubstrate 11 or be located on the upper main face of the substrate 11with equivalent contacting.

Additional to the resonant metallization structure 1 there are at leasttwo further metallization structures on the lower main face of thesubstrate 11, which serve as feeding points 3, 4 for capacitivelycoupling-in the HF power to be radiated.

In accordance with FIG. 1(B) they are a first feeding point 3 as well asa second feeding point 4, which in the area of the first connectingpoint 2 are arranged on opposite edges of the lower main face of thesubstrate 11 in symmetry with the longitudinal axis of the substrate 11.The feeding points 3, 4 then preferably have a distance of about 200 μmfrom the edge of the substrate 11 for reasons associated with themanufacturing. The feeding points 3, 4 are soldered onto correspondingcontact points of the printed circuit board 30 as is the firstconnecting point 2.

The selection of the feeding point 3, 4 for coupling-in the HF power ismade in dependence on the positioning of the antenna on the printedcircuit board 30 concerned.

To improve mechanical load-bearing capacity in case the printed circuitboard 30 is for example bent, and to ensure reliable contact, thesoldering points 5 are further arranged on the lower main face in theregion of the opposite longitudinal end of the substrate 11.

As an alternative to the substrate antenna described above it ispossible to dispense with the substrate particularly with frequencies ofabout 2 GHz and over and to dispose the antenna i.e. the resonantprinted wiring structure, for example directly on the printed circuitboard 30 and to establish the HF connection via capacitive couplingmechanisms, for example, an SMD capacitor on the printed circuit board30. Since the material of the printed circuit board 30 generally has adielectric constant of 4, but also materials for the printed circuitboard having a dielectric constant of about 10 are known, the resonantprinted wiring structure needs to be modified only marginally, inparticular be lengthened.

Antennas of this and similar types are generally arranged such that theyhave an input impedance of 50 Ohms. Normally, also the HF line toconnect the antenna to the transmit and receive stages has aself-impedance or a line impedance of 50 Ohms to achieve asreflection-free and thus loss-free adaptation as possible betweenantenna, HF line and the electronic units connected thereto (finalstages, receiving stages etc.). However, also other antenna and lineimpedances are conceivable.

In the case of the antenna module according to the invention the HF line20 is arranged, for example, as a co-planar line or printed wiring onthe printed circuit board 30. Other embodiments such as, for example,microstrips, strip lines etc. are also possible, however.

The self-impedance of these HF lines 20 can be adjusted by suitableselection of certain parameters such as, for example, their physicaldimensions, more particularly their width, their distance from theground metallization 31 of the printed circuit board 30 and the type andthickness of the material (dielectric constant) used for the printedcircuit board 30.

According to the invention the selection of these parameters is made sothat at least parts or sections 21, 22 of the HF line 20 have amismatch, which means an impedance deviating from the self-impedance ofthe antenna 10. Surprisingly it has appeared that the bandwidth of thewhole antenna module can be considerably enlarged by this.

The bandwidth of the antenna module can then specifically be adjusted bythe selection of the extent of the impedance deviation where theimpedance of the HF line 20 may be larger or smaller than the impedanceof the antenna 10.

There is a particularly strong increase of the resonance bandwidth ofthe antenna module when in the course of the HF line 20 an impedancetransgression or impedance jump, i.e. a relatively steep change of theimpedance, is inserted.

In accordance with FIG. 1(A) such an impedance jump can be achieved, forexample in that a first HF line section 21 adjusted to the inputimpedance of the antenna 10 is connected to the antenna 10 via a secondsection 22 whose line impedance compared to the input impedance of theantenna 10 is about 10 to 25% higher or lower, so that all in all therewill be an HF line 20 mismatch with the antenna.

The FIGS. 2 and 3 show the influence of a mismatched HF line 20 on theresonance bandwidth of the antenna module shown in FIG. 1(A), where theantenna 10 has a self-impedance of 50 Ohms. In the FIGS. 2 and 3 thescattering parameters S₁₁ are plotted against frequency.

In FIG. 2 the resonance curve A shows the case of an adjusted 50 Ohm HFline for comparison. The resonance curve B shows the case of an HF line20 having a self-impedance of 40 Ohms, whereas the resonance curve C wasmeasured for an impedance jump in the HF line 20 from 50 to 40 Ohms (forexample by means of the two line sections 21, 22 shown in FIG. 1(A)).

In FIG. 3 the resonance curve A again shows the case of a matched 50-OhmHF line for comparison. The resonance curve B appears in the case of anHF line 20 having an impedance of 60 Ohms, whereas the resonance curve Cwas measured for an impedance jump in the HF line 20 from 50 to 60 Ohms(which can again for example be realized by means of the two linesections 21, 22 shown in FIG. 1(A)).

A comparison of the two FIGS. 2 and 3 more particularly of the resonancecurves B shows that the resonance bandwidth can be considerablyincreased by an impedance increase to 60 Ohms, whereas there was areduction of the resonance bandwidth for the antenna shown in FIG. 1(B)when there was an impedance reduction to 40 Ohms. However, it ispossible with different antenna designs, for example, such designshaving impedances different from 50 Ohms, to achieve an increase of theresonance bandwidth even when an HF line 20 is used with reducedimpedance compared therewith.

The inclusion of an impedance transition or impedance jump results inthe largest resonance bandwidth for the antenna 10 shown in FIG. 1(B) asshown in the resonance curve 3 in FIG. 3.

The FIGS. 4 and 5 show the effects of the antenna module with thevarious HF lines plotted against frequency.

FIG. 4 shows in curve A the variation of the efficiency in the case of a50-Ohm HF line adapted to the antenna 10. The efficiency shown in curveB is the result of a mismatched HF line 20 with a self-impedance of 40Ohms, whereas curve C shows the variation of the efficiency in the caseof an HF line 20 with an impedance jump from 50 to 40. For the antenna10 shown in FIG. 1(B) there was a lower efficiency in the case of an HFline 20 having an impedance that was reduced compared to that of theantenna.

FIG. 5 correspondingly shows the efficiency curves in the case of amismatch by impedance increase, that is to say compared to the curve Awhich is again used for an adapted 50 Ohm HF line.

Curve B shows the case of an impedance increase to 60 Ohms whereas thecurve C shows the efficiency variation for an HF line 20 with animpedance jump from 50 to 60 Ohms.

FIG. 5 shows that, as a result of the increase of the impedance of theHF line 20 compared to that of the antenna 10, the efficiency evenimproves so that the increase of the resonance bandwidth is not causedby additional losses such as, for example, by reflection.

The curves B and C in FIG. 5 illustrate that also the radiationbandwidth is considerably higher when an HF line 20 is used with 60 Ohmsand particularly such an HF line is used with an impedance transitionfrom 50 to 60 Ohms. The bandwidth was thereby increased by about 30 MHz,which corresponds to a proportional widening by about 30%.

The above values of the line impedances are to be understood merely asexamples. Obviously, also mismatches with different impedance valuesthan in the order of magnitude mentioned above of about 10 to about 25%may be effected while the selection and design in essence depends on thetype of antenna, the frequency range provided and the desired bandwidth.

1. An antenna module, more particularly for the high-frequency andmicrowave range with an antenna (10) and an HF line (20) to connect theantenna (10) to associated transmit and/or receive stages, in which atleast parts or sections (21, 22) of the HF line (20) have a mismatch inthe form of an impedance deviating from the impedance of the antenna(10).
 2. An antenna module as claimed in claim 1, comprising an HF line(20), which has an impedance that is about 10 to about 25% lower orhigher than that of the antenna (10).
 3. An antenna module as claimed inclaim 1, comprising an HF line (20) which has a first and a secondsection (21, 22) which have different impedances and form an impedancetransition or impedance jump which is about 10 to about 25% lower orhigher than the self-impedance of the antenna (10).
 4. An antenna moduleas claimed in claim 1, in which the antenna (10) is a dielectric blockantenna (DBA) or a printed wire antenna (PWA) which is mounted on aprinted circuit board (30), in which the HF line (20) is produced in theform of at least one printed wiring structure deposited on the printedcircuit board (30).
 5. An antenna module as claimed in claim 1, in whichthe antenna is produced in the form of at least one resonant printedwiring structure and is deposited on a printed circuit board (30)together with the HF line (20).
 6. A printed circuit board, moreparticularly for surface mounting electronic elements, comprising anantenna module as claimed in claim
 1. 7. A mobile telecommunicationsdevice, more particularly for the 2.4-GHz range, comprising an antennamodule as claimed in claim 1.